Context:
If the Pro Layouts are not covered by Copyright, then reflecting Open Source is merely a part of Linux Desktop.
The ZorinGroup has mentioned having legal counsel that assisted in creating much of the legaleeze documentation for Zorin OS that can probably offer advice on where this falls.
In the meantime - My opinionated reply:
As Zorin OS Pro is a Convenient Want; that supports development, myself and others have pointed out to many users that complained of Pro on the forum that Layouts is something that they can, if so inclined, set up on Core.